Select All option in rich:datatable

i have a richfaces datatable, where in i will be displaying values in multiple pages with 15 rows per page. i need to include a 'select all' option as the first column in the table.
when the user selects the 'select all' option, all the checkboxes in that particular page should be selected. But the way i have implemented, i am getting all the checkboxes getting selected
including the rows of other pages also. How can this be avoided? Suggestions please..